Production method for semiconductor device

ABSTRACT

A production method for a semiconductor device comprising the first step of supplying a first reaction material to a substrate housed in a processing chamber to subject to a ligand substitution reaction a ligand as a reaction site existing on the surface of the substrate and the ligand of the first reaction material, the second step of removing the excessive first reaction material from the processing chamber, the third step of supplying a second reaction material to the substrate to subject a ligand substituted by the first step to a ligand substitution reaction with respect to a reaction site, the fourth step of removing the excessive second reaction material from the processing chamber, and a fifth step of supplying a third reaction material excited by plasma to the substrate to subject a ligand, not subjected to a substitution reaction with respect to a reaction site in the third step, to a ligand substitution reaction with respect to a reaction site, wherein the steps 1-5 are repeated a specified number of times until a film of a desired thickness is formed on the substrate surface.

This application is a Divisional of co-pending application Ser. No.11/666,360 filed on Apr. 26, 2007 which is a National Stage ofInternational Application No. PCT/JP06/302659 filed on Feb. 15, 2006,the entire contents of which are hereby incorporated by reference andfor which priority is claimed under 35 U.S.C. §120.

FIELD OF THE INVENTION

The present invention relates to a producing method of a semiconductordevice and a substrate processing apparatus.

DESCRIPTION OF THE RELATED ART

To produce a semiconductor device, a thin film such as a dielectricfilm, a metal oxide film or the like is formed on a semiconductorsubstrate at a low temperature by a CVD (Chemical Vapor Deposition)method or an ALD (Atomic Layer Deposition) method.

However, in the thin film formed at a lower temperature (600° C. orlower), problems such as increase in etching speed (when film quality ischecked, the produced film is etched and evaluated, and if the film isnot dense, the etching speed is increased), and film shrinkage when hightemperature process is carried out are generated. Therefore, a methodand an apparatus for producing a high quality film are desired.

SUMMARY OF THE INVENTION

Hence, it is a main object of the present invention to provide aproducing method of a semiconductor device and a substrate processingapparatus capable of forming a high quality thin film even when the thinfilm is formed at a low temperature.

According to one aspect of the present invention, there is provided aproducing method of a semiconductor device comprising: a first step ofsupplying a first reactant to a substrate accommodated in a processingchamber to cause a ligand-exchange reaction between a ligand of thefirst reactant and a ligand as a reactive site existing on a surface ofthe substrate; a second step of removing a surplus of the first reactantfrom the processing chamber; a third step of supplying a second reactantto the substrate to cause a ligand-exchange reaction to change theligand after the exchange in the first step into a reactive site; afourth step of removing a surplus of the second reactant from theprocessing chamber; and a fifth step of supplying a plasma-excited thirdreactant to the substrate to cause a ligand-exchange reaction toexchange a ligand which has not been exchange-reacted into the reactivesite in the third step into the reactive site, wherein the first tofifth steps are repeated predetermined times until a film having apredetermined thickness is formed on the surface of the substrate.

According to another aspect of the present invention, there is provideda producing method of a semiconductor device comprising: a thin filmforming comprising: supplying a first reactant into a processing chamberin which a substrate is accommodated to cause the first reactant to beabsorbed on a surface of the substrate; removing a surplus of the firstreactant from the processing chamber; supplying a second reactant intothe processing chamber to cause the second reactant to react with thefirst reactant adsorbed on the surface of the substrate to form a thinfilm of at least one atomic layer; and removing a surplus of the secondreactant from the processing chamber; and a plasma processing ofsupplying a plasma-excited gas into the processing chamber to improve afilm quality of the thin film after the thin film forming, wherein thethin film forming and the plasma processing are repeated predeterminedtimes until a thin film having a predetermined thickness is formed.

According to still another aspect of the present invention, there isprovided a producing method of a semiconductor device comprising: a thinfilm forming step of repeating the following four steps to form a thinfilm of several atomic layers on a substrate, supplying a first reactantinto a processing chamber in which a substrate is accommodated to causethe first reactant to be absorbed on a surface of the substrate;removing a surplus of the first reactant from the processing chamber,supplying a second reactant into the processing chamber to cause thesecond reactant to react with the first reactant adsorbed on the surfaceof the substrate to form a thin film of at least one atomic layer, andremoving a surplus of the second reactant from the processing chamber;and a plasma processing step of supplying an oxygen atom-containing gasinto the processing chamber to improve a film quality of the thin filmafter the thin film forming step, wherein the thin film forming step andthe plasma processing step are repeated predetermined times until a thinfilm having a predetermined thickness is formed.

According to still another aspect of the present invention, there isprovided a producing method of a semiconductor device comprising: aoxide film forming step of repeating the following four steps to form anoxide film having a desired thickness on a silicon film, supplying afirst reactant into a processing chamber in which a substrate, thesilicon film is exposed from a surface of which, is accommodated tocause the first reactant to be adsorbed onto a surface of the siliconfilm, removing a surplus of the first reactant from the processingchamber, supplying a second reactant into the processing chamber tocause the second reactant to react with the first reactant adsorbed onthe surface of the silicon film to form a thin film of at least oneatomic layer, and removing a surplus of the second reactant from theprocessing chamber; and a plasma nitriding processing step of nitridinga surface of the oxide film using a gas including a nitrogen atom afterthe oxide film forming step.

According to still another aspect of the present invention, there isprovided a substrate processing apparatus, comprising: a processingchamber in which a substrate is to be accommodated; a first supply meansfor supplying a first reactant into the processing chamber; a secondsupply means for supplying a second reactant into the processingchamber; a third supply means for supplying a third reactant into theprocessing chamber; an exhausting means for evacuating the processingchamber; an exciting means for plasma-exciting the third reactant; and acontrol means for controlling the first to third supply means, theexhaust means and the exciting means, wherein the control means controlsthe first to third supply means, the exhausting means and the excitingmeans, to repeat the following first to fifth steps predetermined timesuntil a thin film having a desired thickness is formed; the first stepof supplying the first reactant to the substrate accommodated in theprocessing chamber to cause a ligand-exchange reaction between a ligandas a reactive site existing on a surface of the substrate and a ligandof the first reactant; the second step of removing a surplus of thefirst reactant from the processing chamber; the third step of supplyinga second reactant to the substrate to cause a ligand-exchange reactionto change the ligand after the exchange in the first step into areactive site; the fourth step of removing a surplus of the secondreactant from the processing chamber; and the fifth step of supplying aplasma-excited third reactant to the substrate to cause a ligandexchange reaction to exchange a ligand which has not beenexchange-reacted into the reactive site in the third step into thereactive site.

According to still another aspect of the present invention, there isprovided a substrate processing apparatus, comprising: a processingchamber in which a substrate is to be accommodated; a first supply meansfor supplying a first reactant into the processing chamber; a secondsupply means for supplying a second reactant into the processingchamber; a third supply means for supplying a third reactant into theprocessing chamber; an exhausting means for evacuating the processingchamber; an exciting means for plasma-exciting the third reactant; and acontrol means for controlling the first to third supply means, theexhaust means and the exciting means, wherein the control means controlsthe first to third supply means, the exhausting means and the excitingmeans, to repeat a thin film forming step and a plasma processing steppredetermined times until a thin film having a desired thickness isformed, the thin film forming step comprising: a step of supplying thefirst reactant into the processing chamber in which the substrate isaccommodated to cause the first reactant to be absorbed on a surface ofthe substrate; a step of removing a surplus of the first reactant fromthe processing chamber; a step of supplying the second reactant into theprocessing chamber to cause the second reactant to react with the firstreactant adsorbed on the surface of the substrate to form a thin film ofat least one atomic layer; and a step of removing a surplus of thesecond reactant from the processing chamber, and the plasma processingstep supplying the plasma-excited third reactant into the processingchamber for improving a film quality of the thin film after the thinfilm forming step.

According to still another aspect of the present invention, there isprovided a substrate processing apparatus, comprising: a processingchamber in which a substrate is to be accommodated; a first supply meansfor supplying a first reactant into the processing chamber; a secondsupply means for supplying the first reactant into the processingchamber; an exhausting means for exhausting an atmosphere in theprocessing chamber; a third supply means for supplying an oxygenatom-containing gas into the processing chamber; a plasma means forbringing the oxygen atom-containing gas into a plasma state; and acontrol means for controlling the first to third supply means, theexhausting means and the plasma means, wherein the control meanscontrols the first to third supply means, the exhausting means and theplasma means, to repeat a thin film forming step and a plasma processingstep predetermined times until a thin film having a desired thickness isformed, the thin film forming step comprising: a step of supplying thefirst reactant into the processing chamber to cause the first reactantto be absorbed on a surface of the substrate; a step of removing asurplus of the first reactant from the processing chamber; a step ofsupplying the second reactant into the processing chamber to cause thesecond reactant to react with the first reactant adsorbed on the surfaceof the substrate to form a thin film of one atomic layer; and a step ofremoving a surplus of the second reactant from the processing chamber,and the plasma processing step supplying an oxygen atom-containing gasinto the processing chamber for improving a film quality of the thinfilm after the thin film forming step.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic vertical sectional view for explaining a verticaltype substrate processing furnace in a substrate processing apparatus ofa first embodiment of the present invention.

FIG. 2 is a schematic transverse sectional view for explaining thevertical type substrate processing furnace in the substrate processingapparatus of the first embodiment of the present invention.

FIG. 3 is a diagram for explaining an ALD sequence of the firstembodiment of the present invention.

FIG. 4 is a diagram for explaining the ALD sequence for comparison.

FIG. 5 is a diagram for explaining O₂ plasma processing effect on an ALOfilm in the first embodiment of the present invention.

FIG. 6 is a schematic vertical sectional view for explaining a capacitorstructure to which plasma nitriding processing is applied according to asecond embodiment of the present invention.

FIG. 7 is a diagram for explaining an effect of the plasma nitridingprocessing in the second embodiment of the present invention.

FIG. 8 is a schematic vertical sectional view for explaining a gatespacer to which a third embodiment of the present invention is applied.

FIG. 9 is a schematic vertical sectional view for explaining a liner ofSTI (Shallow Trench Isolation) to which the third embodiment of thepresent invention is applied.

FIG. 10 is a diagram for explaining nitride profiles of plasma nitridingprocessing and thermal nitriding in the third embodiment of the presentinvention.

FIG. 11 is a diagram showing a relation between NH₃ irradiation time anda film stress.

FIG. 12 is a diagram showing a relation between the NH₃ irradiation timeand concentrations of Cl and H in a film.

FIG. 13 is a diagram for explaining a sequence of a conventional ALDfilm forming method and a sequence of an ALD film forming method usingH₂ plasma of a fourth embodiment.

FIG. 14 is a diagram showing a concentration of Cl and a film stress ina film in the ALD film forming using H₂ plasma in the fourth embodiment.

FIG. 15 is a diagram for explaining a sequence of the ALD film formingmethod using H₂ plasma in the fourth embodiment.

FIG. 16 is a diagram showing concentrations of Na in films formed by theALD method and an LPCVD method.

FIG. 17 is a diagram showing a model into which Na existing in a Nastate is taken in the case of irradiation of NH₃ plasma.

FIG. 18 is a diagram showing a model from which Na existing in a Na⁺state is removed in the case of irradiation of N₂ plasma.

FIG. 19 is a diagram showing a relation between plasma irradiation timeand a concentration of Na in a film.

FIG. 20 is a diagram showing a relation between a concentration of Naand plasma-exciting high frequency (RF) power.

FIG. 21 is a diagram showing a result of measurement of distribution ofconcentration of Na by SIMS in a film formed by an ALD method.

FIG. 22 is a diagram showing a result of measurement of distribution ofconcentration of Na by SIMS in a film formed by a LPCVD method.

FIG. 23 is a diagram for explaining a supply method of ionized N₂ gas.

FIG. 24 is a diagram showing a relation between a supply method ofionized N₂ gas and concentration of Na in a film.

FIG. 25 is a diagram showing concentrations of Na in films when anintentionally Na-contaminated wafer is irradiated with NH₃ plasma andwhen an intentionally Na-contaminated wafer is irradiated with N₂plasma.

FIG. 26 is a flowchart for explaining a first step of a sixthembodiment.

FIG. 27 is a flowchart for explaining a second step of the sixthembodiment.

FIG. 28 is a diagram showing a number of foreign matters when a pressureat the time of plasma irradiation in the second step in the sixthembodiment is about 0.3 to 0.4 Torr.

FIG. 29 is a diagram showing a number of foreign matters when a pressureat the time of plasma irradiation in the second step in the sixthembodiment is about 0.5 Torr or higher.

FIG. 30 is a schematic perspective view for explaining a substrateprocessing apparatus according to preferred embodiments of the presentinvention.

FIG. 31 is a schematic vertical sectional view for explaining asubstrate processing apparatus according to the preferred embodiments ofthe present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Next, preferred embodiments of the present invention will be explained.

In the preferred embodiments of the present invention, a film formingoperation and plasma processing are continuously carried out in the sameprocessing chamber to form a high quality film at a low temperature.

By doing like this, an ALD process can also be used easily. In the ALDmethod, a step of supplying a first reactant into a processing chamberaccommodating a substrate therein and for allowing the first reactant tobe absorbed on a surface of the substrate, a step of removing a surplusof the first reactant from the processing chamber, a step of supplying asecond reactant into the processing chamber and for allowing the secondreactant to react with the first reactant adsorbed on the surface of thesubstrate to form a thin film of at least one atomic layer, and a stepof removing a surplus of the second reactant from the processing chamberare repeated a plurality of times, thereby depositing the thin film onthe substrate. In the preferred embodiments of the present invention,the first reactant and the second reactant react with each other on asurface on which a film is to be formed, to form a thin film by oneatomic layer by one atomic layer, and plasma processing is carried outevery one atomic layer to improve the film quality, or the plasmaprocessing is carried out after several atomic layers are formed toimprove the film quality. Since the film quality can be improved byplasma at a low temperature, a problem that a diffusion layer spreads atthe time of high temperature processing is not generated.

In the preferred embodiments of the present invention, plasma of oxygenor oxygen nitride such as O₂, N₂O, NO, NO₂, H₂O is used for the plasmaprocessing. Alternatively, plasma of nitride or nitride hydride such asN₂ and NH₃, or plasma of Ar or H₂ is used.

In the preferred embodiments of the present invention, not onlyembodiments in which the plasma processing is carried out whenever athin film of one layer or several layers is formed by the ALD method,but also embodiments in which the plasma processing is carried out aftera thin film having a predetermined thickness is formed by the ALD methodor before a predetermined thin film is formed by the ALD method areincluded.

In the ALD method, when a case in which TMA (Al(CH₃)₃,trimethylaluminum) and O₃ (ozone) are alternately supplied to form anAl₂O₃ (aluminum oxide) film is considered, if a TMA molecule is adsorbedon a foundation, with methyl groups (CH₃ groups) being coupled to twocoupling hands of an Al atom of the TMA molecule, a methyl group whichis coupled to the remaining one of the coupling hands is eliminated by aligand-exchange reaction with an OH group which is a ligand functioningas a reactive site on a substrate surface, resulting in coupling to thefoundation. If O₃ is supplied in this state, the two methyl groups,which are ligands, are eliminated as H₂O and CO₂ by a ligand-exchangereaction (more specifically, a ligand removing reaction) with O₃ whichfunctions as a ligand removing agent, and OH groups which function asreactive sites are coupled to the two coupling hands of the Al atom ofthe TMA molecule. Thereafter, if TMA molecules are supplied, H atoms ofthe two OH groups (ligand as reactive site) and methyl groups (ligand)of the TMA molecule are coupled to each other by a ligand-exchangereaction to eliminate them as methane molecules, and coupling hands ofthe Al atoms after methyl molecules are eliminated are coupled to two Ogroups from which H atoms are eliminated. The film forming process thusproceeds and Al₂O₃ is formed in this manner. However, if incompleteoxidation reaction (ligand removing reaction) occurs for some reason,even O₃ is supplied for example, only one of the two methyl groupsreacts with O₃ and is eliminated as H₂O and CO₂, and an OH group iscoupled to one coupling hand of the Al atom of the TMA molecule(ligand-exchange reaction), but the remaining one methyl group stays asit is in some cases. If TMA is supplied in such a state, the methylgroup which has not been subjected to the ligand-exchange reaction intoOH group is covered with TMA which is a raw material having highmolecular-weight, and O₃ of next step does not reach the methyl group.If ALD production is continued in this state, the methyl group remainsin the film and depletion is generated in such a portion in some cases.

However, if the substrate is irradiated with O₂ plasma having higheroxidizing performance than O₃, O₂ plasma can enter and reach the methylgroup. As a result, the methyl group is eliminated from the film and isreplaced by OH group, and although slight (about one layer) depositiondelay (surface roughness) is generated as compared with a peripherallocation where reaction normally occurred, the reaction proceeds fromthe OH group from the next processing step, and excellent film qualitycan be obtained. The above-described phenomenon appears after thealternate supply of TMA and O₃ is repeated at least two times (twocycles) and at least the second layer is formed. It is conceivable thatif the plasma processing is carried out whenever one layer is formed(whenever one cycle of gas supply is carried out), most of residualmethyl groups are replaced by OH groups by O₂ plasma, which allows thedeposition to proceed while repairing incomplete oxidization reactionwhenever one layer is formed, resulting in that C ingredient does notremain in the film almost at all.

On the other hand, when a film is formed by a CVD method, since AlxOyproduced by a reaction between TMA and O₃ in a vapor phase falls onto asubstrate and is deposited thereon, even if impurities of intermediateproducts containing C (ex. CO, CO₂, CH₃ and products having highmolecular weight) are taken into the film in addition to Al₂O₃, thedeposition of the film on the substrate proceeds. As a result,impurities are mixed in ten times order as compared with the ALD.Therefore, even if the plasma processing is carried out after a thinfilm of about 1 to 10 μm is produced, the impurities are pulled out fromthe film, and since the amount of the impurities is high, many depletionportions exist in the film. Further, some impurities are not pulled outand C ingredients remain in the film. As a result, even if the plasmaprocessing is carried out after a thin film of about 1 to 10 μm isformed by the CVD method, a film quality is still poor, and there is alimit to the improvement of the film quality.

From the above reason, it is conceivable that a film having much higherquality can be formed if a thin film formation by the ALD method andplasma processing are combined with each other as compared with a casein which the plasma processing is carried out after a thin film of about1 to 10 μm is produced by the CVD method.

Next, embodiments of the present invention will be explained in detailwith reference to the drawings.

First Embodiment

FIG. 1 is a schematic vertical sectional view for explaining a verticaltype substrate processing furnace of a substrate processing apparatus ofthe present embodiment. FIG. 2 is a schematic transverse sectional viewfor explaining the vertical type substrate processing furnace of thesubstrate processing apparatus of the present embodiment.

A reaction tube 203 as a reaction container to process wafers 200 assubstrates is provided inside a heater 207 which is heating means. Amanifold 209, made of a stainless steel and the like, is engaged with alower end of the reaction tube 203. A lower end opening of the manifold209 is air-tightly closed by a seal cap 219 which is a lid through anO-ring 220 which is a sealing member. At least the heater 207, thereaction tube 203, the manifold 209 and the seal cap 219 form aprocessing furnace 202. The reaction tube 203, the manifold 209, theseal cap 219, and a later-described buffer chamber 237 formed in thereaction tube 203 form a processing chamber 201. The manifold 209 isfixed to a holding means (heater base 251).

Annular flanges are provided on the lower end of the reaction tube 203and an upper end opening of the manifold 209. A sealing member (O-ring220, hereinafter) is disposed between these flanges, and the spacebetween the flanges is air-tightly sealed.

A boat 217 which is substrate-holding means stands on the seal cap 219through a quartz cap 218. The quartz cap 218 functions as a holding bodywhich holds the boat 217. The boat 217 is inserted into the processingfurnace 202. A plurality of wafers 200 to be batch processed are stackedon the boat 217 in many layers in an axial direction of the tube intheir horizontal attitudes. The heater 207 heats the wafers 200 insertedinto the processing furnace 202 to a predetermined temperature.

Three gas supply tubes 232 a, 232 b and 232 e are provided as supplytubes through which gas is supplied to the processing chamber 201. Thegas supply tubes 232 b and 232 e are merged into a gas supply tube 232 goutside of the processing chamber 201. The gas supply tubes 232 a and232 g pass through the lower part of the manifold 209. The gas supplytube 232 g is in communication with one porous nozzle 233 in theprocessing chamber 201.

Reaction gas (TMA) is supplied to the processing chamber 201 through amass flow controller 241 a which is a flow rate control means, a valve252 which is an open/close valve, a TMA container 260, and a valve 250which is an open/close valve, and a later-described gas supply section249. The gas supply tube 232 b from the TMA container 260 to themanifold 209 is provided with a heater 300, and the temperature of thegas supply tube 232 b is maintained at 50 to 60° C.

Reaction gas (O₃) is supplied from the gas supply tube 232 a to theprocessing chamber 201 through a mass flow controller 241 a which is aflow rate control means, a valve 243 a which is an open/close valve, thegas supply tube 232 g, the porous nozzle 233 and the later-describedbuffer chamber 237 formed in the reaction tube 203.

Oxygen plasma is supplied from the gas supply tube 232 e to theprocessing chamber 201 through a mass flow controller 241 e which is aflow rate control means, a valve 255 which is an open/close valve, thegas supply tube 232 g, the porous nozzle 233 and the later-describedbuffer chamber 237 formed in the reaction tube 203.

A line 232 c for inert gas is connected to the gas supply tube 232 b ona downstream side of the valve 250 through an open/close valve 253. Aline 232 d for inert gas is connected to the gas supply tube 232 a on adownstream side of a valve 243 a through an open/close valve 254.

The nozzle 233 is provided along the stacking direction of the wafers200 from a lower portion to a higher portion of the reaction tube 203.The nozzle 233 is provided with gas supply holes 248 b through which aplurality of gases are supplied.

The buffer chamber 237 which is a gas dispersing space is provided in anarc space between the inner wall of the reaction tube 203 and the wafers200. The buffer chamber 237 is provided along the stacking direction ofthe wafers 200 and along an inner wall of the reaction tube 203 from alower portion to a higher portion of the reaction tube 203. Gas supplyholes 248 a which are supply holes through which gas is supplied areformed in an inner wall of the buffer chamber 237 near an end portion ofthe inner wall adjacent to the wafers 200. The gas supply holes 248 aare opened toward the center of the reaction tube 203. The gas supplyholes 248 a have the same opening areas over a predetermined length froma lower portion to an upper portion along the stacking direction of thewafers 200, and pitches between the gas supply holes 248 a are equal toeach other.

A nozzle 233 is disposed near another end of the buffer chamber 237 onthe opposite side from the end of the buffer chamber 237 where the gassupply holes 248 a are provided. The nozzle 233 is disposed along thestacking direction of the wafers 200 from the lower portion to thehigher portion of the reaction tube 203. The nozzle 233 is provided witha plurality of gas supply holes 248 b which are supply holes throughwhich gas is supplied.

The gas ejected from the gas supply hole 248 b is ejected into thebuffer chamber 237. The gas is once introduced into the buffer chamber237, which makes it possible to equalize velocities of flows of gases.

That is, in the buffer chamber 237, the particle velocity of the gasejected from each gas supply hole 248 b is moderated in the bufferchamber 237 and then, the gas is ejected into the processing chamber 201from the gas supply hole 248 a. During that time, the gas ejected fromeach gas supply hole 248 b becomes gas having equal flow rate and anequal velocity of flow when the gas is ejected from the gas supply hole248 a.

A rod-like electrode 269 and a rod-like electrode 270 having thin andlong structures are disposed in the buffer chamber 237 such that theseelectrodes are protected by electrode protection tubes 275 which areprotection tubes for protecting these electrodes from the higherportions to the lower portions. One of the rod-like electrode 269 andthe rod-like electrode 270 is connected to the high frequency powersupply 273 through the matching device 272, and the other electrode isconnected to the ground which is a reference electric potential. As aresult, plasma is produced in a plasma producing region 224 between therod-like electrode 269 and the rod-like electrode 270.

These electrode protection tubes 275 have such structures that therod-like electrode 269 and the rod-like electrode 270 can be insertedinto the buffer chamber 237 in a state where the electrodes are isolatedfrom the atmosphere of the buffer chamber 237. If the inside of theelectrode protection tubes 275 is the same as the outside air(atmospheric air), the rod-like electrode 269 and the rod-like electrode270 respectively inserted into the electrode protection tubes 275 areheated by the heater 207 and oxidized. Hence, there is provided an inertgas purge mechanism which charges or purges inert gas such as nitrogeninto the electrode protection tubes 275, thereby sufficiently reducingthe concentration of oxygen, to prevent the rod-like electrode 269 andthe rod-like electrode 270 from being oxidized.

A gas supply section 249 is formed on an inner wall separated from theposition of the gas supply holes 248 a by about 120° along an innerperiphery of the reaction tube 203. The gas supply section 249 is asupply section which shares the gas supply species with the bufferchamber 237 when the plurality kinds of gases are alternately suppliedto the wafers 200 one kind by one kind when films are formed by the ALDmethod.

Like the buffer chamber 237, the gas supply section 249 also has gassupply holes 248 c which are supply holes through which gas is suppliedto positions adjacent to the wafers at the same pitch, and the gassupply section 249 is connected to a gas supply tube 232 b at a lowerportion thereof.

The processing chamber 201 is connected to a vacuum pump 246 which isexhausting means through a valve 243 d by a gas exhaust tube 231 whichis an exhaust tube through which gas is exhausted so that the processingchamber 201 is evacuated. The valve 243 d is an open/close valve, andthe processing chamber 201 can be evacuated and the evacuation can bestopped by opening and closing the valve 243 d. If the opening of thevalve is adjusted, the pressure in the processing chamber 201 can beadjusted.

The boat 217 is provided at a central portion in the reaction tube 203,and the plurality of wafers 200 are placed in many layers at equaldistances from one another in the vertical direction. The boat 217 canbe brought into and out from the reaction tube 203 by a boat elevatormechanism (not shown). To enhance the uniformity of the processing, aboat rotating mechanism 267 which is a rotating means for rotating theboat 217 is provided. By rotating the boat rotating mechanism 267, theboat 217 held by the quartz cap 218 is rotated.

A controller 321 which is a control means is connected to the mass flowcontrollers 241 a, 241 b and 241 e, the valves 243 a, 243 d, 250, 252,253, 254, and 255, the heater 207, the vacuum pump 246, the boatrotating mechanism 267, and a boat elevator mechanism (not shown). Thecontroller 321 controls adjustment operations of flow rates of the massflow controllers 241 a, 241 b, and 241 e, opening and closing operationsof the valves 243 a, 250, 252, 253, 254 and 255, opening and closingoperations of the valve 243 d and adjustment operations of the pressureof the valve 243 d, adjustment operation of the temperature of theheater 207, actuation and stop of the vacuum pump 246, adjustmentoperation of the rotation speed of the boat rotating mechanism 267, andthe vertical motion of the boat elevator mechanism.

Next, as an example of the film forming operation by the ALD method willbe explained based on a case wherein an Al₂O₃ film is formed using TMA,O₃ gas and O₂ plasma. FIG. 3 is a diagram for explaining the ALDsequence of the embodiment. FIG. 4 is a diagram for explaining the ALDsequence for comparison.

First, semiconductor silicon wafers 200 on which films are to be formedare set in the boat 217, and the boat 217 is brought into the processingfurnace 202. After the boat 217 is brought into the processing furnace202, the following five steps are carried out in sequence.

[Step 1]

In step 1, a TMA gas is flown. TMA is liquid at ordinary temperatures.To supply the TMA gas to the processing furnace 202, there are a methodin which the TMA gas is heated and vaporized and then supplied to theprocessing furnace 202, and a method in which inert gas called carriergas such as nitrogen and noble gas is sent into a TMA container 260, andvaporized TMA gas is supplied to the processing furnace together withthe carrier gas. This embodiment will be explained based on the latermethod. First, the valve 252 provided on the carrier gas supply tube 232b, the valve 250 provided between the TMA container 260 and theprocessing furnace 202, and the valve 243 d provided on the gas exhausttube 231 are opened, carrier gas whose flow rate is adjusted by the massflow controller 241 b is supplied from the carrier gas supply tube 232 bthrough the TMA container 260 to be a mixture gas of TMA and the carriergas, and the mixture gas is supplied to the processing chamber 201 fromthe gas supply holes 248 c of the gas supply section 249, and in thisstate the gas is exhausted from the gas exhaust tube 231. When flowingthe TMA gas, the valve 243 d is appropriately adjusted, and the pressurein the processing chamber 201 is maintained at a predetermined pressurein a range of 10 to 900 Pa. A supply flow rate of the carrier gascontrolled by the mass flow controller 241 b is 10,000 sccm or less. Thesupply time of TMA is set to 1 to 4 seconds. Then, time during which thewafer is exposed to the increased pressure atmosphere for furtheradsorption may be set to 0 to 4 seconds. The temperature of the heater207 at that time is set such that the temperature of the wafers becomes250 to 450° C.

If the open/close valve 254 is opened from a line 232 d of inert gasconnected to an intermediate portion of the gas supply tube 232 a toallow inert gas to flow, wraparound of TMA toward the O₃ side can beprevented.

At that time, only inert gas such as TMA, N₂ and Ar flow into theprocessing chamber 201, and O₃ does not exist. Therefore, TMA does notgenerate vapor-phase reaction, and the TMA surface-reacts with afoundation film on the wafer 200.

[Step 2]

In step 2, the valve 250 of the gas supply tube 232 b is closed to stopthe supply of TMA. The valve 243 d of the gas exhaust tube 231 is leftopen, the processing chamber 201 is evacuated by the vacuum pump 246 to20 Pa or lower, and remaining TMA is exhausted from the processingchamber 201. At that time, simultaneously the open/close valve 253 isopened to flow N₂ gas as inert gas from the line 232 c of inert gasconnected to an intermediate portion of the gas supply tube 232 b, andthe open/close valve 254 is opened to flow N₂ gas as inert gas from theline 232 d of inert gas connected to an intermediate portion of the gassupply tube 232 a and N₂ gas is flown into the processing chamber 201.

[Step 3]

In step 3, O₃ gas is flown. First, the valve 243 a provided on the gassupply tube 232 a and the valve 243 d provided on the gas exhaust tube231 are both opened, O₃ gas whose flow rate is adjusted by the mass flowcontroller 241 a is supplied from the gas supply tube 232 a into theprocessing chamber 201 from the gas supply holes 248 a of the bufferchamber 237, and simultaneously the gas is evacuated from the gasexhaust tube 231. When the O₃ gas is flown, the valve 243 d isappropriately adjusted, and the pressure in the processing furnace 202is maintained at a predetermined pressure in a range of 10 to 100 Pa. Asupply flow rate of O₃ controlled by the mass flow controller 241 a isin a range of 1,000 to 10,000 sccm. Time during which the wafers 200 areexposed to O₃ is 2 to 120 seconds. The temperature of the wafer at thattime is the same as the temperature when TMA is supplied and is in arange of 250 to 450° C.

If the open/close valve 253 is opened from the line 232 c of inert gasconnected to an intermediate portion of the gas supply tube 232 b toallow inert gas to flow, wraparound of O₃ gas toward the TMA side can beprevented.

At that time, only inert gas such as O₃, N₂ and Ar flow into theprocessing furnace 202, and TMA does not exist. Therefore, O₃ does notgenerate a vapor-phase reaction, and O₃ surface reacts with a foundationfilm formed by adsorption of TMA on the wafer 200, and an Al₂O₃ film isformed on the wafer 200.

[Step 4]

In step 4, the valve 243 a of the gas supply tube 232 a is closed tostop the supply of O₃ gas. The valve 243 d of the gas exhaust tube 231is left open, the processing chamber 201 is evacuated by the vacuum pump246 to 20 Pa or lower, and residual O₃ is exhausted from the processingchamber 201. At that time, simultaneously the open/close valve 254 isopened to flow N₂ gas as inert gas from the line 232 d of inert gasconnected to an intermediate portion of the gas supply tube 232 a, andthe open/close valve 253 is opened to flow N₂ gas as inert gas from theline 232 c of inert gas connected to an intermediate portion of the gassupply tube 232 b and N₂ gas is flown into the processing chamber 201.

[Step 5]

In step 5, the open/close valve 254 of the line 232 d of inert gas andthe open/close valve 253 of the line 232 c of inert gas are closed tostop the supply of N₂ gas. The valve 255 provided on the gas supply tube232 e is opened, and O₂ gas whose flow rate is adjusted by the mass flowcontroller 241 e is sent from the gas supply tube 232 e into the bufferchamber 237 from the gas supply holes 248 b of the nozzle 233. Highfrequency electric power is applied between the rod-like electrode 269and the rod-like electrode 270 from the high frequency power supply 273through the matching device 272, O₂ is plasma-excited and this issupplied to the processing chamber 201 as active species andsimultaneously the gas is exhausted from the gas exhaust tube 231. WhenO₂ gas flows as the active species by plasma-exciting the O₂ gas, thevalve 243 d is appropriately adjusted and the pressure in the processingchamber 201 is maintained at a predetermined pressure in a range of 10to 900 Pa. A supply flow rate of O₂ controlled by the mass flowcontroller 241 e is a predetermined flow rate in a range of 1 to 10,000sccm. Time during which the wafer 200 is exposed to active speciesobtained by plasma-exciting O₂ is in a range of 0.1 to 600 sec. Thetemperature of the heater 207 at that time is set equal to an AlO filmforming temperature.

Then, the valve 255 of the gas supply tube 232 e is closed to stop thesupply of O₂ gas, and application of the high frequency electric powerfrom the high frequency power supply 273 is also stopped. The valve 243d of the gas exhaust tube 231 is left open, the processing chamber 201is evacuated by the vacuum pump 246 to 20 Pa or lower, and residual O₂gas is exhausted from the processing chamber 201. At that time,simultaneously the open/close valve 254 is opened to flow N₂ gas asinert gas from the line 232 d of inert gas connected to an intermediateportion of the gas supply tube 232 a, and the open/close valve 253 isopened to flow N₂ gas as inert gas from the line 232 c of inert gasconnected to an intermediate portion of the gas supply tube 232 b and N₂gas is flown into the processing chamber 201.

The above steps 1 to 5 are defined as one cycle, and this cycle isrepeated a plurality of times, thereby forming the Al₂O₃ films having apredetermined thickness on the wafers 200 (see FIG. 3).

FIG. 5 shows a result of measurement of leak current of a capacitor filmusing an Al₂O₃ film produced by this embodiment and leak current of acapacitor film using Al₂O₃ formed on a wafer 200 only by repeating thecycle (steps 1 to 4) a plurality of times without carrying out theprocessing using O₂ plasma as shown in FIG. 4. It can be found that ifthe O₂ plasma processing is carried out, the leak current is remarkablyreduced. If the O₂ plasma processing is carried out, it is possible toreduce the leak current, and to reduce EOT (Equivalent Oxide Thickness:film thickness converted into oxide film: film thickness when film isconverted into oxide film based on dielectric constant).

It is preferable that the steps 1 to 5 are defined as one cycle, and theO₂ plasma processing is carried out whenever one atomic layer is formedby the ALD method by repeating the cycle a plurality of times, but it isalso possible to carry out the O₂ plasma processing whenever two to fiveatomic layers are formed by the ALD method. It is not preferable tocarry out the O₂ plasma processing whenever six or more atomic layersare formed because impurities such as carbon compound are not eliminatedeasily even if the O₂ plasma processing is carried out.

In the present embodiment, O₂ gas is supplied from the gas supply tube232 e and the O₂ plasma processing is carried out, but N₂O, NO, NO₂ orH₂O may be supplied from the gas supply tube 232 e instead of O₂ gas andthe plasma processing may be carried out. Further, Ar or N₂ may be usedin the plasma processing.

Second Embodiment

When a capacitor film is to be formed, an Si surface is nitrided andthen an alumina film (Al₂O₃ film) is formed. In this embodiment, as amethod for forming a foundation of the alumina film, plasma nitriding iscarried out.

As shown in FIG. 6, the same apparatus as that of the embodiment 1 isused. the valve 255 provided to the gas supply tube 232 e is firstopened, NH₃ gas whose flow rate is adjusted by the mass flow controller241 e is ejected from the gas supply tube 232 e into the buffer chamber237 through the gas supply holes 248 b of the nozzle 233, high frequencyelectric power is applied between the rod-like electrode 269 and therod-like electrode 270 from the high frequency power supply 273 throughthe matching device 272 to plasma-excite NH₃, which is supplied into theprocessing chamber 201 as a active species and in this state, the gas isexhausted from the gas exhaust tube 231. In this manner, a barrier SiNfilm 402 is formed on a doped polycrystalline silicon 401.

Then, the steps 1 to 4 are defined as one cycle, and the cycle isrepeated a plurality of times, thereby forming the Al₂O₃ film 403 on thebarrier SiN film 402 by the ALD method. Thereafter, a TiN 404 is formedand a capacitor is prepared.

FIG. 7 shows breakdown voltages of a capacitor formed in theabove-described manner and a capacitor prepared by forming the Al₂O₃film 403 directly on the doped polycrystalline silicon 401 withoutforming the barrier SiN film 402. It can be found that the capacitorusing the barrier SiN film 402 formed as in this embodiment hasextremely high breakdown voltage.

Although NH₃ gas is supplied from the gas supply tube 232 e and the NH₃is plasma-excited to form the barrier SiN film 402 in the presentembodiment, N₂ gas may be supplied from the gas supply tube 232 e and N₂may be plasma-excited to form the barrier SiN film 402.

Third Embodiment

In the embodiment, a surface of an oxide film formed by the ALD methodis subjected to plasma nitriding processing. As nitriding processing ofan oxide film of a liner portion of a gate spacer or STI (Shallow TrenchIsolation), thermal processing is conventionally carried out at about800 to 900° C. using oxidizer such as NO and N₂O. Nitrogen distribution,however, is concentrated on an interface between SiO₂ and Si, whichresults in lowering mobility, and thus, a technique for plasma nitridingthe SiO₂ surface has been desired.

A MOS transistor which is one kind of semiconductor devices which arepreferably prepared by applying the present embodiment will be explainedwith reference to FIG. 8. This MOS transistor is formed in a regionsurrounded by an element isolator 412 formed in a silicon layer 411. Agate electrode 430 including a doped polycrystalline silicon 419 and ametal silicide 420 is formed on an oxide film 417 formed on the siliconlayer 411 and a plasma nitride film 418. A gate spacer 421 made of SiO₂is formed on a side wall of the gate electrode 430, and a plasma nitridefilm 423 is formed on the gate spacer 421. The silicon layer 411 isformed with sources 413 and 414 as well as drains 415 and 416 such as tosandwich the gate electrode 430. An insulation film 422 is formed suchas to cover the MOS transistor formed in this manner.

Next, a liner portion of the STI (Shallow Trench Isolation) which ispreferably formed by applying the present embodiment will be explainedwith reference to FIG. 9. A silicon layer 440 is formed with a groove443, and an oxide film 441 made of SiO₂ is formed on the silicon layer440. A plasma nitride film 442 is formed on the oxide film 441. A groove443 is to be filled with an oxide film (not shown) to form the elementisolation region, and the plasma nitride film 442 is formed before theoxide film is formed so that the oxidation does not spread.

In the present embodiment, the same apparatus as that of the firstembodiment was used, TMA in the first embodiment was replaced by DCS(dichlorosilane: SiH₂Cl₂), and O₂ in the first embodiment was replacedby NH₃, respectively. In the case of the MOS transistor, DCS and O₃ werealternately supplied to form a gate spacer 421 having a desiredthickness by the ALD method and then, a surface of the gate spacer 421was plasma nitrided by NH₃ plasma to form the plasma nitride film 423.In the case of STI, DCS and O₃ were alternately supplied to form anoxide film 441 by the ALD method, and a surface of the oxide film 441was plasma nitrided to form a plasma nitride film 442.

In the present embodiment, the surface of the SiO₂ is plasma nitrided inthis manner. FIG. 10 shows a nitrogen profile when the surface issubjected to thermal nitriding processing and the processing of thepresent embodiment. In the present embodiment, nitrogen does not existalmost at all at an interface between Si and SiO₂ at the time of lowtemperature processing at 600° C. or lower and there is a peak ofnitrogen concentration near the surface of the SiO₂, which shows thatthe surface of the SiO₂ can be nitrided.

Although NH₃ gas is supplied and NH₃ is plasma-excited to form theplasma nitride film in the present embodiment, N₂ gas may be suppliedand N₂ may be plasma-excited to form the plasma nitride film.

Fourth Embodiment

To form a silicon nitride film on a Si wafer by the ALD method, NH₃ andDCS (SiH₂Cl₂) are used as raw materials.

Film forming procedure will be shown below.

(1) A Si wafer is transferred onto a quartz boat.

(2) The quartz boat is inserted into a processing chamber having atemperature of 300° C.

(3) When the insertion of the quartz boat is completed, the processingchamber is evacuated, and the temperature in the processing chamber isincreased to about 450° C.

(4) DCS irradiation (three seconds)→N₂ purging (fiveseconds)→plasma-excited NH₃ irradiation (six seconds)→N₂ purging (threeseconds) are defined as one cycle, and this cycle is repeated until apredetermined film thickness is obtained. At that time, the thickness ofthe film formed every one cycle is about 1 Å(=0.1 nm).(5) The reaction gas in the processing chamber is exhausted and thetemperature in the processing chamber is lowered to about 300° C. at thesame time.(6) The pressure in the processing chamber is returned to theatmospheric pressure, and the quartz boat is pulled out from theprocessing chamber.

In semiconductor device structures of recent years, a film stress ofabout 1.8 Gpa is required for moderating distortion, but film stress ofthe film formed through the above-described steps is about 1.2 Gpa,which is lower than the target value.

Therefore, a technique for increasing the NH₃ irradiation time toincrease the stress has been employed. It is possible to increase thefilm stress up to 1.5 Gpa by increasing the NH₃ irradiation time. FIG.11 shows a result of the film stress when the NH₃ irradiation time isincreased. Although the film stress is increased by increasing theirradiation time of excited NH₃, stress of 1.5 Gpa or more can not beobtained.

As stated above, according to the conventional technique of increasingNH₃ irradiation time, the maximum value of the obtained film stress is1.5 Gpa, and it is not possible to achieve the target 1.8 Gpa. If thefilm stress of a nitride film of the transistor section is low, therearise problems including lowering of ON current.

In the present embodiment, the same apparatus as that of the firstembodiment was used, with TMA in the first embodiment replaced by DCS(dichloro-silane: SiH₂Cl₂), O₃ replaced by NH₃ radical and O₂ replacedby H₂, respectively. Then, DCS and NH₃ radical were alternately suppliedto form an Si₃N₄ film with a desired thickness by the ALD method, andthen, the film stress of the Si₃N₄ film was further improved by plasmaof H₂.

A reaction mechanism of the ALD method will be explained below.

(1) First, Si and Cl are adsorbed on a surface by DCS irradiation.

(2) Next, N₂ purge is carried out for replacing the gas (to prevent DCSand NH₃ from being mixed with each other).

(3) Irradiation of excited NH₃ is carried out, to eliminate Cl adsorbedin (1) as HCl, and to allow N and H to be adsorbed.

A cycle of (1) to (3) is repeated until a film thickness reaches apredetermined value.

As a consequence, in addition to Si and N which are main ingredients ofthe ALD nitride film, impurities of H and Cl are taken into the film.

FIG. 12 shows a result of measurement of concentrations of H (hydrogen)and Cl (chlorine) in the film using a SIMS (Secondary Ion MassSpectrometry). It is found that if the NH₃ irradiation time isincreased, the concentration of H is constant but the concentration ofCl is lowered.

Although Cl is taken into a surface from DCS which is a raw material ofCl, Cl is eliminated from the surface in a process of irradiation ofNH₃. Therefore, the NH₃ irradiation time is longer, the eliminatingeffect of Cl is higher, resulting in reducing the concentration of Cl inthe film. However, the concentration of Cl can not be reduced to 1E20(1×10²⁰) atoms/cm³ or lower.

A technique for further lowering the concentration of Cl was researchedon with the assumption that the film stress depends on the concentrationof Cl. When DCS is supplied, Si—Cl bond and Si—H bond exist on a filmsurface. Concerning bonding energy of each of the bonds, the Si—Cl bondhas 397 KJ/mol and the Si—H bond has 318 KJ/mol and thus, the Si—Cl bondhas higher energy. If the film is irradiated with NH₃ radical, the Si—Hbond is replaced by N—H bond, but since the bonding energy of Si—Cl ishigh, the film formation proceed in a state where Cl is included.

To remove the Cl, an experiment for eliminating Cl in a form of HClusing H₂ plasma was carried out.

FIG. 13 shows a sequence of the conventional ALD film forming method anda sequence of the ALD film forming method using H₂ plasma according tothe present embodiment. In both cases, irradiation time of excited NH₃is increased to 20 sec. In the case of the ALD film formation using H₂plasma, the irradiation time of H₂ plasma is 10 sec.

FIG. 14 shows a result of an analysis of the SIMS regarding theconcentration of Cl in films when films are formed by the conventionalALD film forming method and when films are formed by the ALD filmforming method of the present embodiment using H₂ plasma, and shows filmstress with respect to the sequence of the conventional ALD film formingmethod.

From the result of the analysis of the SIMS, it can be found that theconcentration of Cl in the film can be reduced if H₂ plasma is used.

From the result of measurement of the film stress, it is found that ifH₂ plasma is used, the film stress can be increased 1.3 times.

Here, as shown in FIG. 13, the H₂ plasma processing is carried out everycycle, but the same effect can be obtained even if the H₂ plasmaprocessing is carried out once in two or more cycles as shown in FIG.15. FIG. 14 shows a result of the H₂ plasma processing carried out oncein five cycles and ten cycles. In these cases also, it can be found thatthe concentration of Cl in the film is reduced and the film stress isimproved. If the interval of the applications of the H₂ plasmaprocessing is adjusted between one to ten cycles, the film stress canvary.

In FIG. 13, the N₂ purge steps are provided before and after theirradiation of NH₃ radical, but the N₂ purge steps may be omitted. SinceH₂ plasma is generated in the H₂ plasma irradiation step and the NH₃radical irradiation step, it is unnecessary to remove HN₂ by N₂ purge.This is also because that even if electric discharge is thinly turned ONand OFF, it can keep standing.

In FIG. 13, H₂ plasma irradiation is carried out whenever the film isirradiated with either one of DCS and NH₃, the film may be irradiatedwith H₂ plasma only once after irradiation of NH₃ (i.e. irradiated withH₂ plasma every one cycle).

In view of the above result, the same apparatus as that of the firstembodiment was used, with TMA in the first embodiment replaced by DCS(dichloro-silane: SiH₂Cl₂), O₃ replaced by NH₃ radical and O₂ replacedby H₂, respectively. Then, DCS and NH₃ radical were alternately suppliedto form an Si₃N₄ film by the ALD method and then, the Si₃N₄ film wasfurther reformed by plasma of H₂.

Fifth Embodiment

In the present embodiment, the same apparatus as that of the firstembodiment was used, with TMA in the first embodiment replaced by DCS(dichloro-silane: SiH₂Cl₂), and O₃ replaced by NH₃ radical and O₂replaced by N₂, respectively. Then, DCS and NH₃ radical were alternatelysupplied to form Si₃N₄ film by the ALD method and then, the Si₃N₄ filmwas further reformed by plasma of N₂.

To form a silicon nitride film on an Si wafer by the ALD method, NH₃ andDCS (SiH₂Cl₂) are used as raw materials.

Film forming procedure will be shown below.

(1) An Si wafer is transferred onto a quartz boat.

(2) The quartz boat is inserted into a processing chamber having atemperature of 300° C.

(3) When the insertion of the quartz boat is completed, the processingchamber is evacuated, and the temperature in the plasma processing isincreased to about 450° C.

(4) DCS irradiation (three seconds)→N₂ purging (fiveseconds)→plasma-excited NH₃ irradiation (six seconds)→N₂ purging (threeseconds) are defined as one cycle, and this cycle is repeated until apredetermined film thickness is obtained. At that time, the thickness ofthe film formed every one cycle is about 1 Å(=0.1 nm).(5) The reaction gas in the processing chamber is exhausted and thetemperature in the processing chamber is lowered to about 300° C. at thesame time.(6) The pressure in the processing chamber is returned to theatmospheric pressure, and the quartz boat is pulled out from theprocessing chamber.

In a film formed through the above steps, about 3E10)(3×10¹⁰)(atoms/cm³)of Na is included per 100 Å. The concentration of Na was measured usingICPMS (inductive coupling plasma mass analysis method. The value 3E10(3×10¹⁰) is not permitted in the semiconductor industries of recentyears and it is necessary to lower this value.

If Na enters an oxide film of a MOS transistor, this indisposes controlby a gate of transistor output current. Therefore, it is necessary tolower the concentration of Na. In general, a value of about 1E10(atoms/cm³) is required.

When a film is formed by the ALD method and a film is formed by a LPCVD(Low Pressure Chemical Vapor Deposition) method using the sameprocessing chamber, if the concentrations of Na in the formed films arecompared with each other, the detection of Na in the film formed by theLPCVD method is much smaller. FIG. 16 shows the concentrations of Na inthe formed films. The left sides show concentrations of Na when filmsare formed by the ALD method under a condition that high frequencyelectric power is 300 W and the NH₃ irradiation time is 30 seconds. Theright side shows concentration of Na when the film is formed by theLPCVD method at 760° C. In the figure, “TOP” means Si wafer mounted onan upper portion of the quartz boat, “Center” means Si wafer mounted onan intermediate portion of the quartz boat, and “Bottom” means Si wafermounted on a lower portion of the quartz boat. Referring to FIG. 16, itcan be found that the detection of Na in the case of the LPCVD isremarkably smaller.

The ALD method and the CVD method are largely different from each otherin that in the ALD method, NH₃ ionized using plasma and DCS flowalternately, but in the CVD method, DCS and not-ionized NH₃ flow at thesame time.

Focusing on the ionized gas, such a hypothesis is made that Na exists inan ionized state of Na⁺ in a reaction form of Na.

From the comparison between the ALD method and the CVD method, it can bedetermined that Na is not generated from a gas supply system or a dummywafer.

A model in which Na existing in a state of Na⁺ in the reaction form istaken into a film is considered as shown in FIG. 17.

It is assumed that during irradiation of NH₃ ionized by plasma, twokinds of ionized gases, i.e., NH₄ ⁻ (negatively charged) and NH₂ ⁺(positively charged) exist on a surface of a Si wafer. Since Na⁺ isattracted by NH₄ ⁻, Na⁺ can easily be adsorbed in the presence of NH₄ ⁻.That is, while plasma is generated, the Na is prone to be adsorbed.

The following is data attesting to this fact.

(1) FIG. 19 shows a result of the comparison of concentrations of Na infilms by dependency of plasma irradiation time. It can be found that asthe plasma time is longer, the concentration of Na becomes higher. Thatis, since the existing time of NH₄ ⁻ is long, the amount of adsorbed Nais high.(2) FIG. 20 shows a result of the comparison of concentrations of Na infilms by dependency of high frequency (RF) power. It can be found thatas the high frequency (RF) power is higher, the concentration of Nabecomes higher. That is, if the existing amount of NH₄ ⁻ is higher, theamount of adsorbed Na becomes higher.(3) FIG. 21 shows a result of concentration distribution of Na in a filmby SIMS. It can be found that Na is equally distributed in the film.FIG. 22 shows a result of concentration distribution by SIMS of Na in afilm formed by the LPCVD method. It can be found that concentration ofNa is remarkably low in the LPCVD.

From the above results, it can be found that although the location whereNa is generated is not specified (it can also be conceived that Na isgenerated from an electrode which carries out plasma discharge), a modeshown in FIG. 17 in which Na is taken into a film is valid.

In view of the above results, as a countermeasure for reducing an amountof Na taken into a film, a technique for removing the adsorbed Na wasconsidered. To remove Na, it is considered that irradiation of ionizedgas, which is positively charged, after adsorption of Na is effective.As the positively charged ionized gas, N₂ was selected. It is assumedthat N₂ is generating ionized gas of N⁺ by ionization. It is conceivedthat Na⁺ is repelled by N⁺ and detached. See FIG. 18.

FIG. 25 shows a result of the experiment. In FIG. 25, a case in which awafer which has been intentionally contaminated by Na (corresponding to“Ref” in the drawing) is irradiated with NH₃ plasma and a case in whichthe wafer is irradiated with N₂ plasma are compared with each other. Asa result, the concentration of Na was reduced by the irradiation of N₂plasma, and it is conceived that the irradiation of N₂ plasma iseffective.

As a supply method of N₂ ionized gas, studies of a method as shown inFIG. 23 were performed.

TEST0 is a conventional condition without N₂ plasma processing.

An object of TEST1 is to carry out N₂ plasma processing before and afterALD film formation (before and after the cycle is carried outpredetermined times), and to remove adsorption of Na before and afterthe film is formed.

TEST2 is a technique for irradiating a film with N₂ plasma at the sametime during irradiation of NH₃ plasma which is necessary for ALD filmformation and to remove the adsorbed Na in the formed film.

TEST3 is a technique for carrying out N₂ plasma processing every ALDfilm formatting cycle to remove the adsorbed Na in the formed film.

FIG. 24 shows the result.

If attention is paid to TEST1 and TEST3, since N₂ plasma processing iscarried out, a reduction effect of Na can be found.

In the TEST3, the N₂ plasma time is 10 seconds×100 cycles=1,000 seconds(17 minutes) and is longer than that of the TEST1 and thus, it isconceived that the Na concentration reduction effect is higher. In theTEST1, it is conceived that only Na of mainly the film surface isremoved and the amount of Na removed from inside of the film is verysmall. In the TEST3, since the film is irradiated with N₂ plasma everyone cycle, it is conceived that the Na removing efficiency is moreexcellent than TEST1.

In the TEST2, it can be determined that if films are irradiated with NH₃plasma and N₂ plasma at the same time, there is no Na reducing effect.This is because that if negative charge of NH₄ ⁻ exists, the adsorptionof Na proceeds, and in order to remove the adsorbed Na, it is necessaryto once stop the irradiation of NH₃ plasma.

Sixth Embodiment

In the present embodiment, the same apparatus as that of the firstembodiment was used, with TMA in the first embodiment replaced by DCS(dichloro-silane: SiH₂Cl₂), O₃ replaced by NH₃ radical and O₂ replacedby mixture gas of N₂ and NH₃, respectively. Then, DCS and NH₃ radicalwere alternately supplied to form a Si₃N₄ film by the ALD method andthen, the Si₃N₄ film was reformed by plasma of gas mixture of N₂ andNH₃.

More specifically, a film forming step in which a DCS gas irradiationstep and a NH₃ plasma irradiation step are repeated, thereby depositingan SiN thin film of several nm on an Si substrate at a depositing speedof 3 nm/min or higher, and a foreign matter removing step in which inorder to remove foreign matters generated in the first step, plasma gasis generated using mixture gas of N₂ and NH₃ and the Si substrate isirradiated with the plasma gas are repeatedly carried out, therebyreducing contamination caused by foreign matters.

A mixture ratio of mixture gas of N₂ and NH₃ is in a range of 1:1 to6:1, plasma is generated under a pressure of 0.5 Torr, an Si substrateis exposed to the plasma gas, thereby removing foreign matters adheredto the Si substrate.

As one of semiconductor producing steps, an amorphous silicon nitridefilm (SiN, hereinafter) is formed by the ALD method using DCS(dichloro-silane) and NH₃ (ammonia) plasma at a lower substratetemperature of 550° C. or lower. Here, SiN is formed on the substrate byDCS irradiation processing and NH₃ plasma irradiation processing. Byrepeating these two processing (cycle processing, hereinafter), SiNhaving a predetermined film thickness can be deposited on the substrate.However, the ALD method has a defect that a thin film is accumulativelydeposited on a gas-contact portion other than the substrate. Therefore,the following problem is prone to be generated.

The problem is contamination of peeled-off foreign matters caused bygeneration of micro crack of an accumulated film. The foreign mattercontamination is more prone to be generated as the substrate temperatureat the time of SiN deposition becomes lower, as the deposition speedbecomes higher or as the accumulated film thickness becomes thicker.This is because that as the substrate temperature becomes lower or asthe depositing speed becomes higher, the amount of impurities mixed intothe accumulated film increases, the impurities are annealed and detachedby thermal energy caused by continuous film forming processing, microcracks are generated by repeating shrinkage and expansion, and thepeeled-off foreign matter contamination occurs. If the depositing speedis increased, it will easily be affected by the detachment ofimpurities. If impurities are detached during the above described cycleprocessing, a vapor-phase reaction occurs, and vapor phase foreignmatters are prone to be increased. Therefore, this problem poses abarrier for enhancing the apparatus throughput and for improving thefilm quality.

The present embodiment is devised to solve this problem.

The present embodiment comprises the following two steps, and a to-beprocessed substrate is processed by repeating these two steps(conventionally, the SiN was deposited by repeating the first step).

First step: film forming raw material irradiation processing+reformingplasma irradiation processing (corresponding to one cycle processing inthe conventional technique) Second step: foreign matter removing step byplasma

By these two steps, an SiN thin film in which a degree of contaminationof foreign matters is smaller than that of the conventional techniquecan be formed at a high speed. An explanation will be given below as tohow the SiN thin film is formed and how the foreign matters are removedin each of the steps.

First step: (film forming raw material irradiation processing+reformingplasma irradiation processing) One example of a substrate processingflow is shown in FIG. 26.

One cycle of the first step corresponds to one cycle of the 0conventional cycle processing step. In the apparatus shown in FIGS. 1and 2, Si wafers 200 are set in the boat 217, the boat 217 is insertedinto the reaction tube 203, and the heating processing of the substratesin step A1 is started. The processing in step A1 comprises, for example,the following processing. The step may be carried out in accordance withsurface states of the Si wafers 200.

(1) Low Pressure Processing

A pressure in the reaction tube 203 is reduced by the vacuum pump 246,thereby detaching impurities adhered to surfaces of the wafers 200.

(2) Inert Gas Cycle Purge Processing

In this processing, inert gas is introduced into the reaction tube 203having a low pressure through the gas supply tube 232 g at fixedintervals, allowing impurities adhering to the surface of the substrateto be dissolved into the inert gas and to be removed. This processing ispreferably carried out while heating the substrates of the wafers 200.

(3) Plasma Surface Processing (Plasma Surface Oxidation Processing,Plasma Surface Reducing Processing)

In this processing, surface processing gas is introduced into thereaction tube 203 having the low pressure through the gas supply tube232 g and in this state, electric discharge is generated between therod-like electrode 269 and the rod-like electrode 270 by the highfrequency power supply 273 to generate plasma in the buffer chamber 237.With this processing, the wafers 200 are irradiated with theplasma-processed surface processing gas through the gas supply holes 248a formed in the buffer chamber 237. This processing is for removingimpurities adhering to the surfaces of the wafers 200 after the aboveprocessing (1) and (2) is carried out, and the processing is preferablycarried out while rotating the wafers 200 by the boat rotating mechanism267. The surface processing gas at the time of plasma surface oxidationprocessing is mainly O₂, and is reforming gas having a function as anoxidizer. The surface processing gas at the time of plasma surfacereducing processing is mainly H₂, and is reforming gas having a functionas a reducing agent. Supply systems of H₂ and O₂ are not illustrated.

The heating processing is started by inserting the boat 217 into thereaction tube 203. The temperature in the reaction tube 203 ismaintained at a constant value by the heater 207, and the wafer 200 canbe heated and maintained at a predetermined temperature. It is desirablethat the temperature to be maintained is the film forming temperaturesuitable for the film forming raw material as will be described later.

Plasma processing in the later-described step B3 is the same as theabove-described plasma surface processing, and only a gas species to besupplied to the buffer chamber 237 is different.

Next, the processing in steps B1 to B4 is carried out and thin films areformed on the wafers. In the SiN depositing operation using the ALDmethod, it is preferable that, for example, the film forming rawmaterial is DCS and the film forming temperature (wafer temperature) is450° C. or lower. This is because the SiN thin films can be formed oncircuit patterns which are previously formed on the wafers withoutcausing thermal damage and with excellent step coverage.

In the film forming raw material irradiation processing in step B1, afilm forming raw material is adhered to the surfaces of the wafers or areactive intermediate generated in the process of pyrolysis is adheredto the surfaces of the wafers. In the inert gas purge processing in stepB2, the adhered film forming raw material is equalized or component(called component including the intermediate) of the film forming rawmaterial which is not adhered to the surfaces of the wafers isexhausted. In the reforming plasma irradiation processing in step B3,the adhered film forming raw material and the plasma-excited reforminggas react with each other to deposit thin films of atomic layer level.In the inert gas purge processing in step B4, reaction by-productgenerated in step B3 is exhausted from the processing chamber.

Referring to FIGS. 1 and 2, an example in which the film forming rawmaterial is DCS and the reforming plasma is NH₃ plasma will beexplained. In the film forming raw material irradiation processing instep B1, DCS is supplied into the reaction tube 203 through the gassupply tube 232 b. Then, the supply of DCS is stopped in the inert gaspurge processing in step B2 and then, N₂ gas is supplied into thereaction tube 203 through the gas supply tube 232 b. In the reformingplasma irradiation processing in step B3, NH₃ gas is supplied into thereaction tube 203 through the gas supply tube 232 a. During theprocessing in step B3, electric power is supplied to the high frequencypower supply 273 and plasma is generated between the rod-like electrode269 and the rod-like electrode 270. In the inert gas purge processing instep B4, the supply of NH₃ and plasma are stopped and then, N₂ gas issupplied into the reaction tube 203 through the gas supply tube 232 a.By repeating the processing of steps B1 to B4, the SiN thin films havebeen conventionally formed. The formed SiN thin films are amorphous thinfilms comprising elements including Si, N, Cl and H.

Here, in order to enhance the depositing speed of the thin films by theALD method in the first step (corresponding to the conventionalprocessing), it is necessary to shorten the one cycle. In the filmforming raw material irradiation processing in step B1, the film formingraw material causes interaction with a gas-contact portion including thesurface of the substrate to be brought into the adsorption state. Theadsorption state is a state in which a raw material is trapped in a thininteraction layer formed on a surface of the gas-contact portion, and itis assumed that the film forming raw material repeats adsorption anddetachment in the interaction layer to cause the film forming rawmaterial to move. At that time, a portion of the film forming rawmaterial may become an intermediate (e.g., called radical) due to thepyrolysis depending on the temperature of the substrates. When theportion of the film forming raw material becomes the intermediate, sincea molecular structure thereof generally loses electric object andpolarity becomes strong, the interaction (electrical attracting effect)becomes strong and thus, the intermediate does not easily move. When thefilm forming raw material is DCS for example, if the temperature of thesubstrate becomes 450° C. or higher, the amount of producedintermediates is increased, to increase the adsorption amount in onecycle, resulting in increase in the depositing speed. However, themoving speed is reduced and as a result, covering ability of a step isprone to be lost. In the case of DCS, it becomes difficult to producethe intermediate at a low temperature of 400° C. or lower, there is astrong tendency that the adsorption amount (residual amount) becomesconstant, and the depositing speed becomes constant.

However, in the adsorption state, since the adsorption and detachmentare repeated in the interaction layer, the detachment is facilitated bythe inert gas purge in the subsequent step B2. Thus, if the time of stepB2 is increased, the adsorption amount is reduced and the depositingspeed is reduced. Therefore, in order to enhance the depositing speed,it is necessary to shorten the time of step B2. If the time of step B2is shortened, however, the adsorption amount of the film forming rawmaterial, i.e., the residual amount of raw material in the chamber isincreased, and the amount of foreign matters generated by thevapor-phase reaction is increased in the reforming plasma irradiationprocessing in the subsequent step B3. Thus, the supply speed of inertgas in step B2 is increased so that the film forming raw material andthe reforming plasma do not cause a vapor-phase reaction. However, inthe interaction layer, the adsorption molecules of the film forming rawmaterial are not standing still and a portion of the molecules are intheir detaching state. Thus, if the time of step B2 is shortened,foreign matters by the vapor-phase reaction are increased.

As described above, if one cycle time is shortened, foreign matters areincreased and thus, it is difficult to obtain the depositing speed of 3nm/minute or more with the conventional method.

In the present embodiment, in order to solve the problem of theconventional method, the second step for removing vapor-phase reactionforeign matters is carried out subsequent to the first step. It isassumed that in the first step, speed is increased and vapor-phaseforeign matters are generated. An example is shown in FIG. 27.

When the film forming raw material is DCS and the reforming plasma isNH₃, the vapor-phase foreign matters are powder SiN but most of them arenegatively or positively charged by the reforming plasma irradiationprocessing of step B3 in the first step. Since the wafers are negativelycharged, of the vapor-phase foreign matters, only foreign matters whichare positively charged or electrically neutral foreign matters can beadhered to the wafers, and other foreign matters which are negativelycharged can not be adhered to the wafers. In FIG. 27, N₂+NH₃ plasmaprocessing (processing using plasma-excited mixture gas of N₂ gas andNH₃ gas) is for negatively charging the positively charged foreignmatters or neutral foreign matters.

Therefore, after the processing in step C1, since the foreign matters onthe wafer cannot maintain the electrical adhering state, the foreignmatters can be exhausted by the inert gas purge processing in thesubsequent step C2.

Using the apparatus as shown in FIGS. 1 and 2, and using a substrate onwhich about 500 to 900 foreign matters of 0.1 μm were adhered, thereducing width of the foreign matters was measured under the conditionof the second step. FIG. 28 shows a result of the measurement.

From this result, it can be found that the plasma irradiation by mixturegas of N₂ and NH₃ is effective for removing foreign matters. It can befound that even if the mixing ratio is 6:1, there is an effect.

Next, FIG. 29 shows the number of foreign matters of 0.1 to 0.13 μm whena pressure at the time of plasma irradiation is 0.5 Torr or higher.

From this result, it can be found that even in the case of the plasmairradiation of N₂ and NH₃ mixture gas, if the pressure is high, theforeign matter removing effect is lost.

As explained above, in the present embodiment, in the process in whichforeign matters are prone to be generated, i.e., in the thin filmdeposition using high speed ALD method, it is possible to efficientlyremove the foreign matters as compared with the conventional technique.

As described above, according to the preferred first to sixthembodiments of the present invention, a large number of wafers can besubjected to plasma processing collectively, and the film formingprocessing and the plasma processing can be carried out by the integralapparatus. Therefore, the productivity can be enhanced.

Next, an outline of the substrate processing apparatus of the preferredembodiment will be explained with reference to FIGS. 30 and 31.

A cassette stage 105 as a holder delivery member which deliverscassettes 100 as substrate accommodating containers to and from anexternal transfer device (not shown) is provided on a front side in acase 101. A cassette elevator 115 as elevator means is provided behindthe cassette stage 105. A cassette transfer device 114 as transfer meansis mounted on the cassette elevator 115. Cassette shelves 109 asmounting means of the cassettes 100 are provided behind the cassetteelevator 115. Auxiliary cassette shelves 110 are also provided above thecassette stage 105. A clean unit 118 is provided above the auxiliarycassette shelves 110 and clean air flows through the case 101.

The processing furnace 202 is provided on the rear side and at an upperportion in the case 101. The boat elevator 121 as elevator means isprovided below the processing furnace 202. The boat elevator 121vertically brings the boat 217 as the substrate holding means into andfrom the processing furnace 202. The boat 217 holds the wafers 200 assubstrates in many layers in their horizontal attitudes. The seal cap219 as a lid is mounted on a tip end of the elevator member 122 which ismounted on the boat elevator 121, and the seal cap 219 verticallysupports the boat 217. A transfer elevator 113 as elevator means isprovided between the boat elevator 121 and the cassette shelf 109, and awafer transfer device 112 as transfer means is mounted on the transferelevator 113. A furnace opening shutter 116 as closing means whichair-tightly closes a lower side of the processing furnace 202 isprovided beside the boat elevator 121. The furnace opening shutter 116has an opening/closing mechanism.

The cassette 100 in which wafers 200 are loaded is transferred onto thecassette stage 105 from an external transfer device (not shown) in suchan attitude that the wafers 200 are oriented upward, and the cassette100 is rotated by the cassette stage 105 by 90° such that the wafers 200are oriented horizontally. The cassette 100 is transferred from thecassette stage 105 onto the cassette shelf 109 or the auxiliary cassetteshelf 110 by a combination of vertical and lateral motions of thecassette elevator 115, and advancing and retreating motions and arotation motion of the cassette transfer device 114.

Some of the cassette shelves 109 are transfer shelves 123 in whichcassettes 100 to be transferred by the wafer transfer device 112 areaccommodated. Cassettes 100 to which the wafers 200 are transferred aretransferred to the transfer shelf 123 by the cassette elevator 115 andthe cassette transfer device 114.

If the cassette 100 is transferred to the transfer shelf 123, thetransfer shelf 123 transfers the wafers 200 to the lowered boat 217 by acombination of advancing and retreating motions and a rotation motion ofthe wafer transfer device 112, and a vertical motion of the transferelevator 113.

If a predetermined number of wafers 200 are transferred to the boat 217,the boat 217 is inserted into the processing furnace 202 by the boatelevator 121, and the seal cap 219 air-tightly closes the processingfurnace 202. The wafers 200 are heated in the air-tightly closedprocessing furnace 202, processing gas is supplied into the processingfurnace 202, and the wafers 200 are processed.

If the processing of the wafers 200 is completed, the wafers 200 aretransferred to the cassette 100 of the transfer shelf 123 from the boat217, the cassette 100 is transferred to the cassette stage 105 from thetransfer shelf 123 by the cassette transfer device 114, and istransferred out from the case 101 by the external transfer device (notshown) through the reversed procedure. When the boat 217 is in itslowered state, the furnace opening shutter 116 air-tightly closes thelower surface of the processing furnace 202 to prevent outside air frombeing drawn into the processing furnace 202.

The transfer motions of the cassette transfer device 114 and the likeare controlled by transfer control means 124.

The entire disclosure of Japanese Patent Application No. 2005-40501filed on Feb. 17, 2005 including specification, claims, drawings andabstract are incorporated herein by reference in its entirety.

INDUSTRIAL APPLICABILITY

As explained above, according to the preferred embodiments of thepresent invention, there is provided a semiconductor device producingmethod and a substrate processing apparatus capable of forming a highquality thin film when a thin film is formed using the ALD method.

As a result, the invention can suitably be utilized for a producingmethod of a semiconductor device using a semiconductor siliconsubstrate, and a semiconductor silicon substrate processing apparatus.

1. A producing method of a semiconductor device comprising: a first stepof supplying a first reactant to a substrate accommodated in aprocessing chamber to cause a ligand-exchange reaction between a ligandof the first reactant and a ligand as a reactive site existing on asurface of the substrate; a second step of removing a surplus of thefirst reactant from the processing chamber, a third step of supplying asecond reactant to the substrate to cause a ligand-exchange reaction tochange the ligand after the exchange in the first step into a reactivesite; a fourth step of removing a surplus of the second reactant fromthe processing chamber; a fifth step of supplying a plasma-excited thirdreactant to the substrate to cause a ligand-exchange reaction toexchange a ligand which has not been exchange-reacted into the reactivesite in the third step into the reactive site; and repeating the firstto fifth steps until a film having a predetermined thickness is formedon the surface of the substrate.
 2. The producing method of thesemiconductor device as claimed in claim 1, wherein the ligand-exchangereaction in each of the third and fifth steps is a step of carrying outa ligand removing reaction in which the ligand existing at the surfaceof the substrate is removed to form the reactive site.
 3. The producingmethod of the semiconductor device as claimed in claim 1, wherein aligand-exchange reaction is carried out between the reactive sitegenerated as a result of the exchange reaction in the fifth step and theligand of the first reactant supplied in a subsequent first step.